A vehicle drivetrain transfers motive power from a power source to vehicle wheels. An internal combustion engine is one example of a power source that includes a crankshaft. The crankshaft converts combustion energy from engine cylinders into rotational energy. In particular, combustion energy is transferred from the engine cylinders to pistons that linearly reciprocate. The pistons transfer the combustion energy to the crankshaft via rods, and the crankshaft converts the linear motion into rotational motion. The crankshaft may also include main bearing journals that are in mechanical communication with crankshaft bearings. The crankshaft bearings are captured between an engine block and the crankshaft. Lubrication flows from the engine block to the bearings, and the engine block supports the bearings and the crankshaft. The engine block and bearings allow the crankshaft and main bearing journals to rotate within the bearings.
In the design and layout of motor vehicles and internal combustion engines, increasing attention is being paid to vibrations. As part of noise design or sound design, vibrations are balanced, e.g. eliminated or compensated for. In some cases, individual vibrations of a specific frequency are isolated, filtered out or, where applicable, modeled. The crankshaft can be excited to rotary vibration by temporally changing rotary forces which are introduced into the crankshaft via the connecting rods pivoted on the individual crank journals. These rotary vibrations lead to noises both from body-borne sound emission and from body-borne sound introduced into the bodywork and into the internal combustion engine, wherein vibrations can also occur which negatively affect driving comfort, for example, vibrations of a steering wheel in a passenger compartment. When the crankshaft is excited in its inherent frequency range, high rotary vibration amplitudes can occur which can lead to engine degradation.
Attempts to address engine vibrational problems include adding balancing masses to the crankshaft to counteract the forces leading to engine vibration. One example approach is shown by the prior art DE 102013203560 A1. Therein, an internal combustion engine is disclosed including at least one cylinder and including a crank mechanism, in which a crankshaft mounted in a crankcase has an associated crankshaft throw for each cylinder. The crankshaft throws are arranged spaced apart from each other along a longitudinal axis of the crankshaft. At least one balance weight serving as an imbalance is arranged on the crankshaft, on an opposite side to at least one crankshaft throw, for the purpose of mass balancing. Another example approach is shown by U.S. Pat. No. 4,489,683 A in which a balancer, in particular for mass forces of second order, is disclosed for multi-cylinder engines wherein the balancer is arranged between throws of a crankshaft and includes an arrangement of planetary gears with balance units coupled to planet gears. The balancer is shown to include a rotationally fixed internal gear formed from a bulkhead of a crankcase, a rotationally fixed sun gear, and combinations thereof.
However, the inventors herein have recognized potential issues with such systems. As one example, balance weights arranged on a crankshaft may rotate at an un-adjustable rate relative to the rotation of the crankshaft. As a result, the engine vibrational effects at various engine speeds may not be adequately compensated by rotation of the balance weights.
In one example, the issues described above may be addressed by a method for a crankshaft, comprising: a shaft formed about a rotation axis, and at least one connecting rod bearing coupled to the shaft, wherein the crankshaft has at least one balance unit formed from a planetary gear set arranged concentrically to the shaft and at least one un-balanced mass attached to the planetary gear set, wherein the planetary gear set comprises a first stage and a second stage, wherein the first stage has a plurality of first planet gears, a first planet carrier and a first ring gear, and the second stage has a plurality of second planet gears, a second planet carrier and a second ring gear; wherein the shaft is configured as a sun gear of the planetary gear set, and wherein the first ring gear and the second planet carrier are connected together rotationally fixedly, and the at least one un-balanced mass is attached to the second ring gear. In this way, vibrational effects of an internal combustion engine may be compensated by the planetary gear set, and the rotation of the un-balanced mass may be determined via configuration of gear ratios of the planetary gear set. In some embodiments, rotation of the un-balanced mass may be adjustable by directly coupling the planetary gear set to a one-way clutch and a brake. In this way, the un-balanced mass of the planetary gear set may rotate at a rate asynchronous to a rotational rate of the crankshaft, and engine vibrational effects may be effectively compensated for a wide range of engine speeds.
The internal combustion engine with the crankshaft according to this arrangement balances out mass effects of its piston drive which occur in operation. The internal combustion engine therefore has fewer vibrations and in particular decreased rocking about a middle cylinder. The advantages of the internal combustion engine thus benefit a motor vehicle. The improved quietness of running of the internal combustion engine improves driving comfort of the motor vehicle.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.